The purpose of this proposal is to examine specific neuronal identities and mechanisms underlying ocular dominance plasticity of the visual cortex induced by monocular deprivation. It seeks to understand precisely where in the cortical circuit changes are occurring, and whether these changes preferentially affect neurons based on their visual response properties. It will also test whether a specific signaling mechanism governing ocular dominance plasticity during the critical period of peak susceptibility is also required for plasticity that can occur in the adult visual cortex. I will extend recent findings from the lab supporting this proposal using well-established experimental techniques that are currently employed there. Specifically, I will: (1) Identify the cell layers, cell types, and visual response properties of neurons participating in plasticity of the visual cortex following monocular deprivation in both young and adult animals, and compare the precise time course of changes between these two groups. (2) Determine the role of TrkB signaling, which is required for the recovery of cortical responses following reversal of monocular deprivation in critical period animals, in visual cortical plasticity of adult animals. PUBLIC HEALTH RELEVANCE Ocular dominance (OD) plasticity that occurs following monocular deprivation is one of the best studied models for how visual sensory experience and neural activity can actively shape cortical circuits. OD plasticity has been most thoroughly characterized during a developmental window of peak susceptibility defined as the critical period, however, OD plasticity also occurs in adult animals. Understanding the specific mechanisms of OD plasticity in adult animals is important from two perspectives: first, findings in adults would have real clinical significance, as the majority of visual disorders such as amblyopia are more difficult to treat past infancy;and second, a more detailed knowledge of both adult and critical period OD plasticity would provide insights into the features of cortical organization and adaptive rearrangement that differ or are maintained between an adult brain and one undergoing development.